/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.flink.api.connector.source;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.metrics.MetricGroup;

import java.util.Map;
import java.util.concurrent.Callable;
import java.util.function.BiConsumer;

/**
 * A context class for the {@link SplitEnumerator}. This class serves the following purposes:
 * 1. Host information necessary for the SplitEnumerator to make split assignment decisions.
 * 2. Accept and track the split assignment from the enumerator.
 * 3. Provide a managed threading model so the split enumerators do not need to create their
 *    own internal threads.
 *
 * @param <SplitT> the type of the splits.
 */
@PublicEvolving
public interface SplitEnumeratorContext<SplitT extends SourceSplit> {

	MetricGroup metricGroup();

	/**
	 * Send a source event to a source reader. The source reader is identified by its subtask id.
	 *
	 * @param subtaskId the subtask id of the source reader to send this event to.
	 * @param event the source event to send.
	 */
	void sendEventToSourceReader(int subtaskId, SourceEvent event);

	/**
	 * Get the current parallelism of this Source. Note that due to auto-scaling, the parallelism
	 * may change over time. Therefore the SplitEnumerator should not cache the return value
	 * of this method, but always invoke this method to get the latest parallelism.
	 *
	 * @return the parallelism of the Source.
	 */
	int currentParallelism();

	/**
	 * Get the currently registered readers. The mapping is from subtask id to the reader info.
	 *
	 * @return the currently registered readers.
	 */
	Map<Integer, ReaderInfo> registeredReaders();

	/**
	 * Assign the splits.
	 *
	 * @param newSplitAssignments the new split assignments to add.
	 */
	void assignSplits(SplitsAssignment<SplitT> newSplitAssignments);

	/**
	 * Assigns a single split.
	 *
	 * <p>When assigning multiple splits, it is more efficient to assign all of them in a single
	 * call to the {@link #assignSplits(SplitsAssignment)} method.
	 *
	 * @param split The new split
	 * @param subtask The index of the operator's parallel subtask that shall receive the split.
	 */
	default void assignSplit(SplitT split, int subtask) {
		assignSplits(new SplitsAssignment<>(split, subtask));
	}

	/**
	 * Signals a subtask that it will not receive any further split.
	 *
	 * @param subtask The index of the operator's parallel subtask that shall be
	 *                signaled it will not receive any further split.
	 */
	void signalNoMoreSplits(int subtask);

	/**
	 * Invoke the callable and handover the return value to the handler which will be executed
	 * by the source coordinator. When this method is invoked multiple times, The <code>Coallble</code>s
	 * may be executed in a thread pool concurrently.
	 *
	 * <p>It is important to make sure that the callable does not modify any shared state, especially
	 * the states that will be a part of the {@link SplitEnumerator#snapshotState()}. Otherwise the
	 * there might be unexpected behavior.
	 *
	 * <p>Note that an exception thrown from the handler would result in failing the job.
	 *
	 * @param callable a callable to call.
	 * @param handler a handler that handles the return value of or the exception thrown from the callable.
	 */
	<T> void callAsync(Callable<T> callable, BiConsumer<T, Throwable> handler);

	/**
	 * Invoke the given callable periodically and handover the return value to the handler which will
	 * be executed by the source coordinator. When this method is invoked multiple times, The
	 * <code>Coallble</code>s may be executed in a thread pool concurrently.
	 *
	 * <p>It is important to make sure that the callable does not modify any shared state, especially
	 * the states that will be a part of the {@link SplitEnumerator#snapshotState()}. Otherwise the
	 * there might be unexpected behavior.
	 *
	 * <p>Note that an exception thrown from the handler would result in failing the job.
	 *
	 * @param callable the callable to call.
	 * @param handler a handler that handles the return value of or the exception thrown from the callable.
	 * @param initialDelay the initial delay of calling the callable.
	 * @param period the period between two invocations of the callable.
	 */
	<T> void callAsync(Callable<T> callable, BiConsumer<T, Throwable> handler, long initialDelay, long period);

	/**
	 * Invoke the given runnable in the source coordinator thread.
	 *
	 * <p>This can be useful when the enumerator needs to execute some action (like assignSplits) triggered
	 * by some external events. E.g., Watermark from another source advanced and this source now be able to
	 * assign splits to awaiting readers. The trigger can be initiated from the coordinator thread of
	 * the other source. Instead of using lock for thread safety, this API allows to run such externally
	 * triggered action in the coordinator thread. Hence, we can ensure all enumerator actions are serialized
	 * in the single coordinator thread.
	 *
	 * <p>It is important that the runnable does not block.
	 *
	 * @param runnable a runnable to execute
	 */
	void runInCoordinatorThread(Runnable runnable);
}
